Ski trimming lock



Sept. 23, 1941. w. ARMSTRONG SKI TRIMMING LOCK Filed Feb. l5, 1940 2 Sheets-Sheet 2 Patented Sept. 23, 1941 2,256,540 sin TRIMMING Loox William Armstrong, New York, N. Y., assignor to The Dowty Corporation, Wilmington, Del., a

corporation of Delaware Application February 15, 1940, Serial No. 319,072

7 Claims.

This invention relates to a ski trimming lock for locking the landing skis on airplanes while in flight and for allowing unrestrained pivoting of the skis while the airplane is on the ground either during landing or in taxiing. Due to the great increase in the speeds of airplanes during the last few years with resultant increase in air loads and moments, the aerodynamic force exerted on the skis during flight is comparable to the loads and moment exerted on the ski while the airplane is on the ground. The present invention provides a means for positively locking the ski against pivotal movement during flight but allows free pivotal movement when on the ground.

It has been heretofore proposed to use springs or other resilient means such as shock cord attached on opposite sides of the pivotal center of the ski and to the extensible member of the shock absorbing strut. The use of such external spring loaded trimming device is disadvantageous because with the present high speeds of ight, a very strong spring is necessary to make the trimming stable in night. rlhis entails the disadvantages of the excessive weight and space required for such springs and the difliculty of getting the tail of the airplane down on the landlng.

The principal object of the present invention is to provide a positive ski flight lock in which the ski is automatically locked upon taking off but is automatically unlocked by the Weight of the airplane upon landing.

Another object is to provide a ski lock which is fully automatic in action and which depends for its operation upon the extension of the undercarriage strut which takes place immediately after take-oli and which is locked by the compression of this strut upwardly towards the airplane body upon landing.

Another object is to provide a ski lock of the foregoing type which is simple in construction, yet very eifective in operation, which is light in weight, and which Oilers a very low resistance in the air.

Another object is to provide a ski lock which provides the necessary freedom of motion in either direction between the airplane and the ski while on the ground, thereby allowing the airplane to taxi or to land with the tail up or down and/or over rough terrain. At the same time, the amount of freedom is maintained within the vprescribed limits so that the ski is positively Another object is to provide a ski lock of the foregoing typ'e wherein one of the cooperating locking members is provided with inclined surfaces for automatically guiding the other locking member to the locked position on the take-01T.

Still other objects will more fully hereinafter appear.

In the accompanying drawings:

Fig. 1 is a side elevation of a portion of an airplane equipped with one form of ski trimming lock embodying the principles of the present invention.

Fig. 2 is a detailed View of the trimming lock with the device in locked position during flight.

Fig. 3 is a vertical sectional View on the line 3-3 of Fig. 2.

Fig. l is a View showing the position of the locking pin and of the shock absorber cylinder when the airplane is on level ground with the tail up.

Fig. 5 is a similar view with the tail down.

Fig. 6 is a similar View with the front of the ski tilted forwardly as by passing upwardly over an obstruction on the ground.

Figs. 7 and 8 portray a modication, Fig. 7 showing the modification locked in night, and Fig. 8 showing it on the ground with the tail of the airplane down.

Referring to the drawings in detail, l designates an airplane body having the downwardly extending undercarriage comprising a tubular member 2 which constitutes the exterior casing of a shock absorber and encloses the extensible strut 3 having the piston head 4 operating within the cylindrical inner Wall of the member 2 and engaging the shock absorber spring 5. The lower end of the tubular member 2 is sealed by the annular sealing member E5. The piston head 4 is provided with a vertical port 'I interconnecting the spaces above and below the head 4. rFhus, as the strut 3 is compressed or telescoped upwardly within the tubular member 2, the air above piston head 4 is compressed and is gradually allowed to pass through port 'l into the space below piston head 4. It will be understood that insteadof the shock absorber system thus shown diagrammatioally, any other suitable system of shock absorbing may be employed such as hydraulic shockabsorber devices such as oleo struts, shock cord landing gear, or the like, the type of shock absorber not being material to the present invention as'long as it isadapted to normally tendV to force the strut 3 downwardly away from the airplane andto yieldingly allow this strut 3 to be compressed upwardly towards the airplane while the airplane is on the ground.

A ski 8 is pivotally mounted at the lower end of each strut 3, this ski 8 being provided with the usual pedestal 9 which surrounds the pivot pin I carried transversely of the lower end of strut 3.

The locking mechanism itself comprises the pair of lockingplates II cooperating with the locking pins I2 projecting fiXedly from each side of the tubular member adjacent the lower end thereof. Each of the locking pins I2 is received within openings provided therefor in the locking plates II. The locking plates II are rigidly cartion of Figs. 1 and 5, the pin I2 being intermediate the top and bottom of the locking opening and being adapted to swing in an arc of the greatest amplitude. When taxiing with the tail down, the ski is free to pivot at least on each side of this position. When a take-off is made, the upward movement of the tail causes the parts to assume the position shown in Fig. 4 in which the strut 3 and the ski 8 are capable of at least 15 of relative rotation in either direction. As the weight of the airplane is taken off the ski 8, the

Y' shock absorber spring 5 operates to force the ried by the skis 8 in any suitable manner as, Afor Y example, by welding them tol the sidesl of the pedestal 9. The opening in locking plate I I is generally diamond-shaped and is formed by cutting outa portion of the locking plate in such manner as to leave sufficient metal on all sides of the opening to give the necessary strength. The upper portionr of the opening is formed on the rear by the downwardly angularly inclined wall I3 and on the Vfront by the downwardly angularly inclined wallk I. These walls I3 and I4 converge upwardly, coming together at the uppermost portion I5 of the opening, this portion I5 being adapted to receive the locking pin I2 in locking relationship. The slope of the walls I3 and lli provides for guiding the pin I2 into its locking position I5 as the take-off occurs.

VThe portionof the opening below the locking portion I5 is relatively large as compared with the locking pin I2 and allows considerable freedom of the locking pin I2 when the locking pin I2 is moved downwardly toward the ski 8 as by the weight of the airplane. The greatest freedom is provided intermediate of the opening in plate II. The lower portion of the opening is formed bythe inclined lower front wall I5 and the rear wall I "I, these walls being connected at their bottom by the horizontal portion I8. The contour of the front portion of the opening formed by theiront walls I4 and I 6 is such as to Ygive the required freedom to .the locking pin I2 and thereby to the airplane to allow the airplane tail to move upwardly or to allow the front of the ski to move upwardly while the airplane is on the ground. The contour of the rear portion of the opening is such as to give a considerably greater range of movement of the pin I2 from its vertical position rearwardly relative to the ski 8. This is for the reason that when the tail of the airplane is on the ground as during a three point landing, the pin I2 will normally assume the position of Fig. 5 and it is still necessary to provide the necessary freedom rearwardly of the pin so as to Yallow the ski to tilt so as to move its front downwardly as required in passing over the terrain. In practice, the locking opening is so designed that when the strut 3 is vertical, that is, with the tail of the airplane up as in Fig. 4, the strut 3 is capable of 15 forward movement and at least 15 rearward movement, actually 30 of rearward movement. When the airplane is on the ground with the tail down as in Fig. 5, the strut 3 still is capable of 15 movement rearwardly relative to the ski. It will beunderstood that the opening in the locking plate may be designed to control the angles of trim kwithin any required amountthe figures given being those of the R. C. A. F. Specication M 2/38. The operation of the device of Figs. 1 to 6 is as follows:

, When the airplane is on the ground with its tail down, the locking members assume the posistrut 3 downwardly, thereby causing the pin I2 to assume a position above its position shown in surfaces I3 and I4. As the take-01T occurs, the strut 3 is forced outwardly still further and causes the pin I2 to ride along the guiding surfaces I3 or It, and to attain its i'lnal position as shown in Fig. 2 in which the ski 8 is locked so as to be parallel to the line of flight. It will be understood that as the pin I2 attains its iinal position, it moves in an undulating path because the roughness of the terrain causes the ski 8 to pivot asit passes over the ground. Upon making a three point landing, the impact of the ski 8 `with, the ground immediately causes compression v,of the shock absorber spring 5 and motion ofthe strut 3 upwardly into the cylinder 2. This causes the pin I2 to immediately assume a position downwardly and rearwardly of its lockedposition at I5. The design is suchthat the slightest contact of the ski with the ground imparts some freedom to the pin I2 so that undue bending or breaking of the ski is prevented. As the airplane completes the landing, the pin I2 moves downwardly still further until it assumes the position shown in Figs. 1 and 5 wherein the full weight of the airplane is rested upon the strut 3 and the ski 8.

If during landing or taxiing the ski encounters an obstruction causing its nose to rise, the parts will attain the position shown in Fig. 6l in which the ski is shown as being upwardly tilted aboutV are reversed, the lockingv plate I9 being xedlyg mounted as by welding upon the tubular member 2 and the locking pin being xedly mounted upon an ear 25 extending upwardly from the pedestal` 9 on each side of the strut 3 between the strut 3 and the locking plate I 9.

The opening in the locking plate I9 has a somewhat different shape than the opening in the locking plate described above, but givesthe same action. The locking position is designated as 22.

The forward lower side of the locking opening` is designated as 23 and is inclined at a relativelyvr great angle. The rear lower wall 24 of the locking opening is inclined at a considerably less,

angle and serves toflimit downward movement of the front of the ski. These walls 23 and 24 guide the pin 2I into its locking position 22 as before. The upper portion lof the locking opening is formed by the forward wall 25 andthe rear wall 25, these walls being connected at their.

upper portion by the horizontal portion 2'I. The `posltion of maximum freedom of the pin 2I is,

Fig. 4 and to ultimately strike one of the guiding The locking pin 2IV projects outwardly from the ear 2E) into the open-v' ing of the locking plate I9 and is guided thereby.`

as before, intermediate the top and the bottom of the locking slot and in this position the pin has at least motion in either direction whether the tail be up or down. The operation of the modification of Figs. 7 and 3 is identical with that described above, the extension of the strut 3 occurring upon take-off, causing the pin 2l to be pushed downwardly and, if necessary, along a guide wall 23 or Z into the final position 22 which holds thel ski 8 locked against fluttering or pivoting during ight.

From the foregoing description, it will be seen that the present invention provides a tapered lead into the iinal locking position which prevents jamming on extension of the strut 3 and which insures that the ski will be positively locked in the same position immediately upon take-off. It will further be seen that the design is such that the possibility of jamming or breaking of the landing gear upon landing is prevented since the compression of the strut immediately allows freedom of motion of the locking pin. In addition, it will be seen that the invention provides a further advantage in that the ski is considerably restrained in its motion at light strut loads, that is, near full extension of the strut. It will be seen that the invention provides in a simple and economical manner for the positive locking of the ski against fluttering or pivoting during flight while providing for the required amount of freedom when the plane is on the ground. Numerous other advantages of the present invention will be readily apparent to those skilled in the art.

It will be understood that numerous modifications may be made in the devices illustrated herein without departing from the spirit of inventive thought. For example, frictional or hydraulic damping means may be provided for damping the pivoting of the ski. The slotted member l I or i9 may be employed for the attachment of a fairing for streamlining the joint between the member 2 and the ski 8 during flight. The invention may be applied to the main undercarriage ski, to tail skis, 0r to the ski employed at the front of a tricycle undercarriage. Under certain circumstances, the principles of the invention may be applied to elongated landing members other than skis such as, for example, a tandem wheeled landing gear in which a pair of tandem wheels are mounted on a single pivoted connecting member. Other modications may be made in the device and the invention is to be construed as limited only as required by the prior art and as set forth in the appended claims.

I-Iaving thus fully described my invention, what I claim as new and desire to secure by Letters Patent is:

l. In an airplane landing gear, an undercarriage strut, shock absorber means interposed between said strut and the airplane, a ski member pivotally mounted on the lower end oi said strut, a fixed member associated telescopically with said strut, a latch plate carried by one of said members and having an opening, and a locking member xedly carried by the other of said members and received within said opening, said locking member being relatively small compared to said opening, and said opening having a relative wide portion and having sides which converge from said wide portion towards said other of said members to form a narrow central portion which lockingly receives said locking member when said strut is extended.

2. In anv airplane landing gear, a landing gear strut, shock absorber means between said strut and the airplane tending to distend said strut, a landing ski pivotally mounted on the lower end of said strut, locking means rigidly mounted on the airplane, and cooperating locking means r'igidly mounted on said ski, said locking means comprising a latch plate and a relatively small locking pin mounted one on said ski and the other on the airplane, said latch plate having a relatively large opening therein receiving said locking pin, said opening tapering outwardly on both sides from a locking point on its end away from the member on which said locking pin is mounted towards said member on which said latch plate is mounted and thereby kforming angularly inclined sidewalls for guiding said locking pin to said locking point as said strut is distended.

3. In an airplane landing gear, a landing gear strut, shock absorber means between said strut and the airplane tending to distend said strut, a landing sin pivotally mounted on the lower end of said strut, a telescoping member rigidly mounted on the airplane and vtelescopically associated with said strut, a pair of latch plates fixedly mounted on one of said ski and said telescoping member and extending along each side of said lower end of said strut, and a pair oi locking pins iixedly carried by and projecting laterally from the other of said ski and said telescoping member, each of said latch plates having an opening therein receiving one of said locking pins, said 'opening having sides which diverge from the end of said opening adjacent the fixed end of said latch plate to a relatively wide central portion and .thence converge to a locking point on the opposite end of said opening.

4. In an airplane landing gear, a landing gear strut, shock absorber means between said strut and the airplane tending to distend said strut, a landing ski pivotally mounted on the lower end of said strut, a telescoping member rigidly mounted on the airplane and telescopically associated with said strut, a pair of latch plates xedly mounted on one of said ski and said telescoping member and extending along each side of said lower end of said strut, and a pair of locking pins iixedly carried by and projecting laterally from the other oi said ski and said telescoping member, each of said latch plates having an opening therein receiving one of said locking pins, said opening having sides which diverge from the end of said opening adjacent the fixed end of said latch plate to a relatively wide central portion and thence converge to a locking point on the opposite end of said opening, the angle of divergence and of convergence of one side of said opening being substantially greater than that of the other side of said opening.

5. In an airplane landing gear, a strut telescopically mounted on the airplane, .shock absorber means between the strut and the airplane, a ski pivotally mounted on said strut, a locking pin rigidly mounted on the airplane, a latch plate rigidly mounted on said ski and having an opening receiving said pin, said opening having upwardly converging side walls which converge at their uppermost point to a locking point for receiving said locking pin when said strut is fully distended, said side walls guiding said pin from its normal position when the weight of the airplane is upon the ski to said locking point.

6. An airplane ski lock comprising a locking plate and a locking pin, said locking plate having `an opening receiving said pin, one of said plate 7.A An airplane ski lock comprising a locking 10 plate rigidly mounted on the airplane and a locking pin rigidly mounted on the ski, said locking plate having an opening therein receiving said locking pin, said opening having sides which 'converge downwardly away from the airplane to-Y Wards the ski and merging to form a locking point for receiving said pin for guiding said pin into said locking point.

WILLIAM ARMSTRONG. 

